MARINE MOLLUSCA OP THE UNITED STATES. 181 



3. N. EXPANSA, Reeve. Figs. 481, 482. 



Belcher's Arctic Voy. 397, t. 33, f. 2. 1855. 

 N. Bellotii, Adams, Zool. Proc. 51. 1856. 



Sliell^ large, ovate-triangular, tumid, the surface distinctly nu- 

 cleated wiih ridges, both dorsal areas with fine radiating strife; 

 ten teeth in front and fifteen behind the beaks. Dark chestnut 

 colored. 



Length 14, height 9 mill. 



Canadian waters, northward. ( Eur. ) 

 This may be only a very large flourishing state of N. tennis. 



4. N. INFLATA, Hancock. Figs. 483, 484. 



Ann. Nat. Hist. 333, t. 5, f. 13, 14. 1846. 



Shell trapeziform, inflated, thin, coarsely concentrically striate ; 

 interior margin simple ; hinge with five teeth before and ten 

 behind the large oblique ligament cavity ; epidermis yellowish- 

 green. 



Length 7.5, height 6.25 mill. 



Labrador, northwards. 



5. N. DELPHINODONTA, Mighels. Figs. 485-487. 



Bost. Journ. Nat. Hist., iv. 40, t. 4, f. 5. 1842. 



Shell minute, obliquely triangular, beaks raised, nearly terminal ; 

 hinge with three anterior and seven posterior teeth ; epidermis 

 olivaceous. 



Length 3.25, height 2.75 mill. 



New England, northwards. 



Undetermined Species. 



N. EADIATA, De Kay. Moll'. N. York 179, t. 12, f. 21G. 1843. 

 Dredged in E. River, N. Y. The figure is not recognizable. 



Genus LEDA, Schumacher. 

 Essai Nov. Syst. 1817. 



The animal is furnished with two partially united, slender, un- 

 equal siphoual tubes; gills narrow, plume-like, deeply laminated, 

 attached throughout; mantle-margin with small ventral lobes, 

 forming by their apposition a third siphon. 



The typical group comprises about 80 species, inhabiting Arctic 

 and northern seas, 10 to 180 fathoms. 



1. L. TENUISULCATA, Couthouy. Figs. 488, 489. 



(Nucula.) Bost. Journ. Nat. Hist., ii. 64, t. 3, f. 8. 1838. 

 Nucula minuta, Gould, Invert. Mass., edit. i. 101. 1841. 



Shell ovate-lanceolate, produced, narrowed and rostrated behind, 



